The present invention generally relates to aerodynamic control systems. More particularly, it relates to trajectory control systems for high-speed, unguided projectiles.
Requirements exist for an unguided projectile having a flat trajectory flight capability. For example, in military applications an anti-tank weapon system is a lightweight, hand-held weapon capable of launching an explosive-laden projectile directly at a vehicle target located at a moderate distance. Preferably, the projectile should possess good armor penetration capability and fly a flat trajectory. Existing weapon systems of this type employ low projectile launch velocities which result in lofted trajectories. This in turn requires the user to make time-consuming range estimates and subsequent launcher adjustments. Unfortunately, these launcher adjustments are inaccurate since it is very difficult to estimate range to better than 30 percent. Thus, this substantially reduces the first round hit probability of the system.
Flattening of the trajectory of a projectile fired from a hand-held launcher can be accomplished by increasing the launch velocity of the projectile and/or by employing projectile lift. There is, however, a limit on the permissible velocity increase because of the recoil factor. For example, if the desired vertical drop of a five-pound projectile at a target range of 250 meters is one foot, then the launch velocity would have to be increased to approximately 3300 ft/sec. This is far in excess of the capability of any existing or planned, hand-held launching system. Thus, until a far superior recoil and blast abatement system is conceived and built, the direct means of achieving a flat trajectory, namely, greatly increased initial velocity, will have to be held in abeyance.
Alternative methods of achieving a flat trajectory include providing the projectile with lift and lift combined with increased initial launch velocity, the latter permitting design tradeoffs between launch velocity and the size of the lifting surfaces required. These alternative methods, however, present their own set of problems. In the design of a lifting projectile, the lift force should be equal to the weight of the projectile, and means must be provided for orienting and maintaining this lift force in the vertical direction.
Lift can be generated easily by using wings, fins, body asymmetries, jets, etc. Orientation of the lift vector, however, is a much more difficult problem. Because of manufacturing asymmetries of the stabilizer and of lifting surfaces, the projectile will develop significant roll displacements in flight. The resulting roll rates can be large since the axial moment of inertia of these projectiles is extremely low, varying in the range of 0.0012 to 0.0025 slug feet squared. Controlling the roll of the lift vector, then, is a major problem in the design of lifting projectiles for flat-trajectory flight. In the interest of providing a lifting projectile that is simple and inexpensive, the more costly active roll control systems are not attractive in comparison to the simple, passive and semiactive types of roll control systems. Active control systems employ sensors to produce signals to regulate the control surfaces in response to motion outside of a predetermined, acceptable range. Passive control systems employ fixed-orientation control surfaces which are not self-correcting in response to a motion deviation and semiactive systems incorporate into the control surfaces a predetermined amount of corrective control, usually via mechanical means.
Methods of controlling or minimizing the roll displacement of the projectile can be categorized as follows: (a) roll minimization, (b) roll resistance, (c) aerodynamic roll stabilization techniques, (d) attitude stabilization, (e) gravity orientation, (f) gyro-orientation, and (g) ballutes and streamers. Each of these methods possesses limitations when applied to roll control of a lifting projectile launched from a hand-held weapon system, such as inadequate or improper roll control, complexity, too expensive, or introduction of other aerodynamic control problems.
The present invention provides an unguided projectile, particularly useful with hand-held launcher weapon systems, which effectively flies a flat trajectory, is simple in design and easy to use in the field, and obviates the problems considered hereinabove which exist in current projectiles of similar application. The herein-described projectile achieves a flat trajectory by the generation of aerodynamic lift to counter the effect of gravity. The lifting device is stabilized in roll by a simple, displacement type gyroscope directly linked to the lifting section of the projectile. The lifting device and the gyroscope are both mounted on bearings to permit free rotation of the projectile body relative to the roll-stabilized lifting device for lift orientation independent of projectile attitude.
The present invention is related to copending application Ser. No. 649,615, filed Jan. 14, 1976 by Michael A. Brown et al., entitled "Adapter Assembly For Flat Trajectory Flight".